Mike, I am in Missoula and it gets a tad chilly here as well, been wondering the same thing as you......i figure, it cant hurt to put that battery either on a tender and / or keep it a bit warmer than the 20 degree temps my garage can fall to.
What part of Idaho are you in? I ride Idaho alot in the summer, just love it.
I live a few miles east of Ashton, first town south of Island Park. I ride a lot in Montana and love riding there as you do in Idaho (perhaps a case of "the grass is always greener...."?). Actually, we are both fortunate to have such beautiful riding country right out of our garages. I always try to do at least one long ride in Montana each year, and last fall my wife an I did a ride from home up the Front Range, then east to the Bear Paw Battlefield monument, and then a meandering route home. If you are in this area please don't hesitate to contact me.
I'm on Happy Trails email list and by coincidence this morning there was a piece from them on winterizing in my inbox. I've copied and pasted the text below. I'm sure it's all good advice but I certainly don't do all of those things, but perhaps I should do more than I do.
From Happy Trails:
<<Every year we use our motorcycles from early spring until late fall, some with little to no maintenance, others with little more than a chain-lube, a clean air filter, and fresh oil and filter. Over the years we've put on several clinics in early winter to cover the things most riders fail to take care of. We have seen KLR, DR and DRZ swing arm bolts that had to be destroyed, as water and grime had caused corrosion which made removing them impossible.
The rear suspension needs to be cleaned and lubed. Wheel and steering head bearings should be checked and lubed. You might say, "Hey, my bike is new and doesn't need it for awhile." It has been our experience that all bikes have a universal lack of lubrication from the factory.
No matter what bike you ride the information here will be helpful for you, as most bikes have the same general points to cover.
1) Wheel bearings: Are they the OEM non-sealed type? How are the bearing seals? Most non-sealed wheel bearings have very little grease in them. After a few water crossings or overzealous cleaning with a power sprayer there's no grease left. If you remove the OEM wheel bearings I recommend you have new bearings on hand and ready to go. Grease your new wheel bearings before installing.
2) Steering Head: Check the front forks before removing them. If there is play in the steering head they need to be replaced. If you do not have a bearing press, have a shop make these repairs for you. If the bearings are good, then clean them, grease them and reinstall the steering head per service manual instructions.
3) Front forks: Now is a great time to service your front forks. If you don't have a service manual, get one before starting this process. Disassemble and inspect the forks. The bushings at the joint of the fork tubes have a Teflon coating; if they are showing a copper color replace them. Clean and inspect the forks, refill them to the correct level with the correct weight oil, and then reassemble. Note that your fork oil should be replaced on a yearly basis.
4) Rear suspension: Disassemble the rear swing arm; remove and inspect the rear shock. This is a great time to have the shock serviced, which should be done by a suspension expert. Clean and lube the shock absorber linkage. If the needle bearing grease is clean and not contaminated I recommend re-lubing without cleaning the old grease out. Be careful with the needle bearings, because if you lose one you need to replace the kit. When removing the swing arm bolt take care not to damage the threads. These bolts can become corroded over time causing them to seize up and making them extremely difficult to remove. If you encounter this, soak it with penetrating oil and let it sit. Note that getting it out may take several attempts. There are bearings inside the sleeve that need to be lubed. These are also needle bearings, so if they need to be cleaned be very careful. When everything is cleaned and lubed start your reassembly.
5) Antifreeze: Change the coolant in your bike.
6) Drive train: Check the final drive fluid and change if needed. Clean, check and lube the chain and sprockets.
7) Cables: Inspect, clean and lube all cables.
Brakes: Check brake pads and change brake fluid. Inspect the calipers, looking for excessive wear on one side and not the other. If they are not functioning properly you may need to clean and lube them or have them rebuilt.
9) Fuel: If you are storing your bike, use a good fuel stabilizer. It also helps to use a good non-ethanol gas when storing a bike.
10) Batteries: If the bike is not being ridden on a regular basis, use a battery tender to extend the life of the battery.
11) Tools: Depending on the type of bike you have you may need Torx bits, Allen wrenches, Phillips head and flat head screw drivers, a rubber or plastic mallet, bearing and race drivers, Metric wrenches and sockets, a Torque wrench and a shop manual.
12) Supplies: Cable lube, waterproof grease, anti freeze, fuel stabilizer, shop towels and cleaning solvent.>>